Student Learning Objectives.
1. Identify five factors involved in soil formation.
2. Describe different types of parent material.
3. Explain topography and how it affects soil
formation.
4. Explain how organisms affect soil
development.
5. Describe how time and weathering affect
properties of soil.
6. Explain how climate affects the development
of soil.
Terms.
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Alluvium
Bedrock
Chemical weathering
Climate
Glacial till
Loess
Native vegetation
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Organic matter
Outwash
Parent material
Physical weathering
Prairie soils
Timber soils
Topography
What are five different factors that
affect soil formation?
1. Parent material—type of rock material the soil is
formed from.
2. Climate—temperature and moisture
characteristics of the area in which the soil was
formed.
3. Living organisms—the organisms, including plant
material, that live within the soil.
4. Topography—slope characteristics of the soil.
5. Time or weathering—age of the soil and its
climate.
What are some different types of parent
material that affect soils?
 Parent materials are formed by the disintegration
and decomposition of rock.
 They are classified according to the way they were
moved and scattered.
 Many soils have been formed from material
originally moved by glaciers.
 Soils of glacial origin are classified as
follows:
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1. Loess —occurred from the blowing of the soil
after the glaciers melted and dried. Loess is the
most desirable single soil parent material. This is
due to its well-balanced mineral content, medium
texture, and excellent water-holding capacity.
2. Outwash —occurred when the glaciers
melted. The melt waters carried the gravelly
materials away to be deposited below the glacial
ridges. Sandy outwash was carried further
downstream and the finer materials, silt and clay,
were deposited in lakebeds or slow moving
water along streams.
 3. Glacial till —have not been layered from the
effects of wind or water as the other two types of
glacial soils. It often contains a variety of sizes of
soil particles. Pebbles and various sizes of
boulders are common in till.
 Some soils are formed as a result of recent
sediments deposited by streams as they
flood.
 It is referred to as alluvium.
 Alluvium is generally a water-borne
material deposited on bottomlands.
 Bedrock —shale, sandstone, or limestone
bedrock; weathered bedrock can provide soil
 parent material.
 Organic matter —occur where formerly shallow
ponds supported swamp vegetation. The wet
conditions slowed decay of the dead plants so that
organic matter could accumulate.
 The two types of organic soils are referred to as
peat and muck. Muck is more decomposed than
peat.
What is topography and how does it
affect the development of soil?
 Topography refers to the slope characteristics of
a soil. It includes the degree or steepness, length,
shape, and direction of a slope. These factors
influence the amount of rainwater runoff, or the
amount that enters the soil or collects in small
depressions on the soil surface.
 Soils on steep slopes have higher amounts of
runoff and erosion than those on level topography.
 The amount of moisture in the soil during its
development affects the rate of weathering and the
development of subsoil colors.
How do living organisms affect the
development of soil?
 Organisms that live in soil—like plants, insects,
and microbes—actively affect soil formation.
 The greatest affect on the development of soil is
from plants that once grew in it. This is referred to
as native vegetation.
 It determines the kind and amount of organic
matter in the soil.
 For example, two common types of native
vegetation in the Midwest are tall prairie grass and
deciduous-hardwood forests. Soils in these areas
are referred to as prairie soils and timber soils.
What is weathering? How does weathering
and time affect soil?
 There are two types of weathering:
1. Physical weathering —the effects of climatic
factors such as temperature, water, and
wind. Freezing and thawing is a major contributor
to physical weathering.
2. Chemical weathering —changes the chemical
makeup of rock and breaks it down.
Rainwater is mildly acidic, and can slowly dissolve
many soil minerals. Some minerals
react with oxygen in the atmosphere. Oxidation
further acts to decompose rock.
Weathering causes soil to:
 1. Develop—occurs rapidly, plant nutrients are
released, and organic matter accumulates.
 Soils will develop faster in humid regions than in
arid regions.
 2. Mature—soil is at peak productivity with a high
amount of organic matter. Water begins leaching
away nutrients and plant growth starts to decline.
This results in less organic matter.
 3. Age—minerals continue to break down and clay
is leached into the subsoil. The soil becomes
lighter in color from less organic matter.
How does climate affect soil development?
 Climate refers to rainfall, freezing, thawing, wind,
and sunlight.
 A. These factors are either directly or indirectly
responsible for the breakdown of rocks and
minerals, the release of plant nutrients, and many
other processes affecting the development of soils.